1. Field of the Invention
The present invention relates to a broadcast receiver that can selectively receive a digital broadcast and an analog broadcast.
2. Description of the Related Art
Cable television is in widespread use in North America. The user can select a desired one of plural channels to watch a program of the selected channel. In North America, in addition to an analog broadcast which is conventionally used, a digital broadcast which is typified by a BS (Broadcasting Satellite) digital broadcast or a CS (Communication Satellite) digital broadcast is becoming pervasive. In such a digital broadcast, as compared with an analog broadcast, the image quality can be improved higher and the number of channels can be increased. In North America, furthermore, a digital broadcast (terrestrial digital broadcast) which is standardized by ATSC (Advanced Television Systems Committee) has been started. In a digital broadcast, a broadcast signal is transmitted with using a physical channel which is different from that of an analog broadcast, and bands between channels of an analog broadcast are allocated to channels of the digital broadcast. Namely, channels of a digital broadcast exist mixedly with those of an analog broadcast. In the case of channel Nos. 1 to 10, for example, channel allocation is conducted so that channels. 1, 3, 4, 5, 8, and 10 are channels of an analog broadcast, and channels. 2, 6, 7, and 9 are those of a digital broadcast.
In an analog television broadcast, a broadcast station transmits an uncompressed television broadcast signal of one channel on one signal of one physical channel (one frequency band). When it is detected that the user conducts an operation of selecting a channel of the analog broadcast, a broadcast receiver first receives a broadcast signal of the frequency band corresponding to the selected channel, and then immediately outputs video and audio signals to a display apparatus. Therefore, substantially no time period elapses from the timing when the operation of selecting the channel is conducted on the broadcast receiver, to that when an analog broadcast signal of the channel is reproduced on the display apparatus, so that the user can immediately view a program of the channel.
By contrast, in a digital television broadcast, a broadcast station applies compression coding on signals of plural channels by using a digital compression technique, and then transmits the signals in one physical channel (one frequency band) in a time-division manner. Specifically, a digital-television broadcast station multiplexes signals into a signal of one frequency band, and then transmits television broadcast signals of plural channels which are called subchannels. The digital-television broadcast station further transmits a signal containing channel information required for restoring a signal of a desired channel, every two or three seconds with adding the signal to the compressed and multiplexed digital broadcast signal.
When it is detected that the user conducts an operation of selecting a channel, a broadcast receiver first receives a digital broadcast signal of the frequency band corresponding to the selected channel, and then extracts the channel information signal contained in the received signal. On the basis of the channel information signal, the broadcast receiver then separates and extracts a signal of the selected channel from the received digital broadcast signal, restores the signal to the original or uncompressed state, and outputs the restored signal to a display apparatus. After the user conducts an operation of selecting a channel on the broadcast receiver, therefore, the user must wait for about five to ten seconds before a broadcast signal of the channel is reproduced on the display apparatus. During this time period, the user must view the screen of the broadcast receiver on which no image is displayed or no signal is reproduced. In the broadcast receiver, where a digital broadcast signal of one physical channel is received and video and audio signals of a certain subchannel are once output to a monitor apparatus, when an operation of changing a channel is conducted so as to output another subchannel of the physical channel to the monitor apparatus, video and audio signals of the subchannel are immediately output to the monitor apparatus.
Conventionally, a broadcast receiver has bee proposed in which the time period required for channel tuning in a situation where a digital broadcast and an analog broadcast mixedly exist can be shortened (for example, see JP-A-2001-24537 (pages 2 and 3, FIGS. 1 and 2)).
In the broadcast receiver disclosed in JP-A-2001-24537, in order to select a desired one of plural channels to view a program, the user can conduct channel selection on the broadcast receiver by using an inputting device such as a remote controller. Specifically, the user operates a numeric keypad of the remote controller to input a channel number, so that the channel to be viewed can be quickly selected. Alternatively, the user may operate a channel up/down key to sequentially switch over channels while displaying programs on a display apparatus to check the programs, so that a favorite program can be selected.